急性のphenytoin中毒症状発現後に小脳萎縮と持続性の運動失調を呈した一例

Cerebellar Atrophy and Persistent Cerebellar Ataxia after Acute Intoxication of Phenytoin

　急性に出現した高度のphenytoin（PHT）中毒症状が9週間持続した後，頭部CTで病前にはみられなかった小脳萎縮の出現が確認された症例を報告した。意識障害，眼振などの症状は血中濃度の正常化とともに消失したが，体幹，四肢の運動失調は12カ月以上持続した。年余にわたって中毒域のPHT血中濃度が持続する慢性例以外にも，高度の急性中毒症状が数週間持続することによって，不可逆的な小脳障害が出現する可能性があることを指摘した。

Chronic intoxication of phenytoin (PHT) is a well known cause of cerebellar atrophy or irrever-sible cerebellar ataxia. Little attention, on the other hand, is paid for acute PHT intoxication because its clinical signs are believed to be reversible. We here report a patient with acute PHT intoxication, which resulted in irreversible cerebellar ataxia with radiologically definite cerebellar atrophy.

A 39-year-old man admitted to our hospital because of cerebellar ataxia and confusional state. He had been treated with PHT for convulsive sei-zures after receiving craniotomy for left parietal brain abscess 9 years before. The concentration of his serum PHT had been 4 to 7μg/ml because he had frequently omitted taking drug, and the dose of PHT had been increased to 600 mg/day one year before. He had admitted to another hospital 2 months before for left Bell's palsy and had been obliged to take drug regularly. Cerebellar signs andconfusion had gradually developed for 7 weeks. On admission to our hospital, he was awake but in severe confusional state with slurred speech and nystagmus. His serum PHT was 86μg/ml, which returned to therapeutic range 2 weeks after the discontinuation of PHT. His consciousness normal-ized and nystagmus disappeared. However, slurred speech continued and neurological examination revealed postural tremor and severe limb ataxia. During the subsequent 10 months, his cerebellar signs showed minimal improvement. Computed tomographies of his brain on 3rd and 5th month after the onset of his cerebellar dysfunction showed the definite cerebellar atrophy which had not been noted on the CTs 7 months before and 7 weeks after the onset.

Our present observation and a review of literature suggested that not only chronic medication or into-xication of PHT but also several weeks of severe acute intoxication may resulted in irreversible cere-bellar degeneration and ataxia. Thus, we empha-size the underestimated harmfullness of acute PHT intoxication in clinical practice.